The Portal Tomb of Wateresk (Irish: Uachtar Easca – also known as Slidderyford Dolmen) stands a few kilometers northeast of Newcastle, approximately 50 meters west of the A2 road (Dundrum Road) in County Down, Northern Ireland. Portal tombs are megalithic structures found on the British Isles, characterized by two equally tall, upright stones with a door stone in between, forming the front of a chamber partially covered by a massive, slanting capstone.

This Neolithic dolmen (3000 to 2000 BC) consists of two supporting stones and the capstone. The remaining portal stones were shaped to embrace the capstone, a characteristic feature of some megaliths in County Down.

The cuboid menhirs of Ballyloughlin stand approximately 300 meters away, at the edge of Flush Road.